Designers of cargo containers have long faced many related challenges in the design of container sidewalls. First, the structural integrity of the overall container depends on the rigidity and strength of the sidewalls. Second, the sidewalls are optimally light in weight to reduce the transportation costs for the overall container.
Third, government regulations or industry standards often limit the exterior dimensions of cargo containers. Thus, to maximize the capacity of the container, designers of cargo containers seek to minimize the width of the walls of the container without compromising the structural integrity of the container.
Fourth, because cargo containers are repeatedly loaded and unloaded, the interior walls of the container must be resistant to the repeated impact of vehicles and implements used to load and unload the container, and must also optimally be free of protrusions and snag points that could impede the loading or unloading of the container. Fifth, means for securing and dividing cargo within a container are often desirable, and may be provided by incorporating logistics slots in the sidewalls of the container. Other considerations, including the cost and availability of the sidewall components and the ease of manufacturing the sidewalls, are also important.
These challenges are particularly acute in the design and construction of sidewalls for over-the-road trailers. Structural integrity for trailers is of course essential to the safe transportation of goods and materials on public highways. This structural integrity has conventionally been provided by vertical posts or ribs incorporated in the sidewalls of the trailer. In this prior art design, known as “sheet and post” construction, the vertical posts are typically formed by bending or roll forming galvanized steel or extruding aluminum into a hat shaped channel, thus providing rigidity and strength for the vertical post. Relatively thin sidewall panels, typically made of plywood or plastic, are attached to the vertical posts in the interior of the trailer and a protective outer skin, typically made of very thin aluminum, is attached to the vertical posts on the exterior of the trailer. A protective metal, wood or plastic liner may be provided at the base of the interior sidewall to protect the panels and posts from being damaged or pierced by vehicles loading and unloading the trailer.
This conventional design offers certain advantages, including high structural strength attributable to the vertical posts, readily available components, low cost and ease of manufacturing, among others. Also, although the thin interior panels are susceptible to damage, these panels are relatively inexpensive and easy to replace. Conventional sheet and post designs, however, suffer from a key disadvantage, namely, the thickness of the posts required to provide structural integrity for the trailer.
Current state and federal regulations limit the exterior width of a trailer to 102.38 inches. Conventional sheet and post sidewalls are typically at least 1.5 inches thick for each wall, leaving about 99 inches in interior width across the trailer. Several alternatives have been developed to decrease the thickness of trailer sidewalls and maximize trailer capacity. Typically, these designs dispense with the need for reinforcing posts by utilizing relatively thick sidewall panels that provide the structural integrity for the container body. These structural panels, made of solid aluminum or composite steel and plastic, are joined at their edges with vertical splicer plates on the inside and the outside of the trailer. This construction, which reduces the thickness of the trailer sidewalls to less than 0.625 inches each, has increased industry demand for trailers with an interior width of at least 101 inches, an unattainable goal for conventional sheet and post designs.
Although the increased capacity of trailers constructed with structural panels is a definite advantage, and the use of these designs is particularly suited for certain applications, these designs suffer from several disadvantages. For example, solid aluminum panels are expensive, difficult to fabricate and extremely heavy, leading to increased fuel costs in operation. In addition, the plates and rivets necessary to join these panels create snag points on the interior of the trailer which create problems when loading and unloading the trailer.
Composite panels are constructed of a core plastic material and an outer skin of aluminum or steel. Although lighter in weight than solid aluminum panels, composite panels are more expensive than the materials used in conventional sheet and post designs. To address the problem of snag points on the interior of the trailer, composite panels are typically coined at their side edges, or constructed with an offset at their side edges, so that the vertical splicer plate may be recessed from the interior surface of the composite panel. This process also increases the cost of using composite panels for trailer sidewalls. Aluminum and composite structural panels are also difficult and expensive to replace if a single panel becomes damaged in use.
Despite the increased expense and other disadvantages, aluminum and composite structural panels remain advantageous for certain applications. However, the need for cargo container sidewalls that combine the advantages of thin sidewalls with the advantages of sheet and post configurations has been recognized.
U.S. Pat. No. 6,607,237 issued to Wolfgang Graff and Thomas Huddle discloses a sheet and post sidewall configuration with a thickness less than 0.625 inches. This configuration includes relatively thin sidewall posts, interior plastic sheets that interconnect with adjacent posts and an exterior skin attached the posts. The thin sidewall posts disclosed in the '237 patent, however, are necessarily less rigid than the thicker posts utilized in conventional sheet and post designs and offer much room for improvement in the rigidity of a thin sidewall post configuration. Thus, the need remains for a highly rigid, yet thin, sidewall post for use in a sheet and post sidewall construction.
Also, in some embodiments of the invention disclosed in the '237 patent (FIGS. 2, 3, 6 and 14), the edges of the interior plastic sheets are inserted between the outer bent edges of the post and the exterior skin of the sidewall. In this embodiment, as graphically shown in FIG. 1 of the '237 patent, the vertical recesses of the post and the attachment rivets are exposed to the interior of the trailer. Thus, the interior wall of the trailer is not smooth and contains potential snag points.
In other embodiments of the invention disclosed in the '237 patent (FIGS. 4, 5, and 7), the vertical recesses of the post are covered by the edges of the interior plastic sheets. However, in these embodiments, the plastic sheet is secured to the post by small channels on the rear (exterior) surface of the plastic sheet. Although potentially effective at securing the plastic sheet to the posts in a static environment, this configuration is necessarily less effective for securing the plastic sheet to the posts when the trailer is subjected to dynamic loads and stresses in operation, let alone the expected impact of vehicles when the trailer is loaded and unloaded. Thus, the need remains for a thin walled sheet and post configuration that securely attaches the sheets to the post while providing a uniform surface on the interior of the trailer without potential snag points.
Accordingly, an object of the present invention is to provide a sidewall construction for a cargo container that is lightweight yet rigid and strong.
A further object of the present invention is to provide a cargo container with thin sidewalls to maximize the capacity of the container.
Yet another object of the present invention is to provide a cargo container with interior walls resistant to the impact of vehicles and implements used to load and unload the container and also free of protrusions and snag points that could impede the loading or unloading of the container.
An additional object of the present invention is to provide a cargo containers with panels that can be easily removed and replaced in the event that they do become damaged.
A still further object of the present invention is to provide a cargo container with interior logistics slots in the sidewalls of the container for securing cargo loaded into the container.
Still another object of the present invention is to provide a highly rigid, yet thin, sidewall post for use in a sheet and post sidewall construction.
Yet another object of the present invention is to provide a thin walled sheet and post configuration that securely attaches the sheets to the post while providing a uniform surface on the interior of the trailer without potential snag points.
Finally, an object of the present invention is to provide a cargo container sidewall configuration that that is economical to manufacture and refined in appearance.